The present invention relates to a digital tuner having a function of receiving a digital broadcast and outputting a received signal to a bus such as an IEEE 1394 serial bus and, more specifically, to a technique for sending an information signal from a tuner subunit as a functional unit in a digital tuner to an external apparatus or receiving an information from an external apparatus.
There have been proposed systems in which electronic apparatuses such as a digital video cassette recorder, a digital tuner, a monitor, and a personal computer are connected to each other via an IEEE 1394 serial bus (hereinafter referred to as "1394 serial bus" and transmission and reception of information signals such as a digital video signal and a digital audio signal and control signals such as an electronic apparatus operation control command and a connection control command are effected between the electronic apparatuses.
In the above-mentioned systems, for example, to display a data stream separated by a digital tuner on a monitor, it is necessary to set an information signal connection between a tuner subunit as a functional unit in the digital tuner and a monitor subunit as a functional unit in the monitor via a 1394 serial bus and to send a signal to the monitor subunit.
As for the information signal connection, the present inventors previously proposed a logical plug concept (see U.S. patent application Ser. No. 354,119 filed on Dec. 16, 1994). A logical plug proposed therein indicates a serial bus plug, i.e., an information signal inlet/outlet in a unit with respect to the 1394 serial bus. Similarly, a plug concept for prescribing an information signal inlet/outlet in a subunit as a functional unit in a unit is introduced. Therefore, although there exists a means for setting a logical connection between a tuner subunit of a digital tuner and a serial bus output plug of a tuner unit, no means is prescribed that sends or receives an information signal to or from a logical plug of a subunit.